1. Field of the Invention
The present invention relates to a prosthesis for preventing gastric reflux in the esophagus, including a valve associated with an annular fixation portion and having an opening that is elastically kept closed.
2. Description of the Related Art
Esophagitis is caused by chronic gastric reflux. Although the mucus of the stomach is capable of withstanding the highly acid pH of the gastric secretions, which is close to 1, this is not the case for the mucus of the esophagus. Consequently, when this reflux is chronic, it attacks the mucus of the esophagus and creates ulcers, which over the long term can cause shrinkage of the esophageal conduit.
This gastric reflux is generally associated with a hiatal hernia. The most currently used therapy for this type of affliction makes use of medicines. There are three categories: antacids, which tend to make the environment neutral by the intake of an alkaline product, H.sub.2 antihistamines, which fix on the H.sub.2 receptor of the parietal cell. Recently, a new medicine has been proposed that in turn blocks the production of H.sup.+ ions by the parietal cell. However, this medicine has no further effect as soon as it ceases to be administered, and it cannot be taken continuously, because it might cause tumors, which has been confirmed at least for the rat. Finally, the third class comprises medicines that increase the motility of the esophagus and the stomach and tend to reduce the length of contact of the acid reflux with the esophagus. This therapy does not attack the primary cause of the ailment, which is gastric reflux, which reappears as soon as the treatment with medicine stops, so that the patient is forced to take medication permanently. This solution is clearly unsatisfactory both medically and economically.
As an alternative to this medication route, it has already been proposed to use an external prosthesis for mechanical opposition to gastric reflux. This external prosthesis is formed by an elastically extensible ring disposed around the end where the esophagus discharges into the stomach. By thus surrounding the base of the esophagus, the centripetal force that this ring exerts offers a flow resistance that tends to prevent gastric reflux from rising in the esophagus. Nevertheless, the effect of this ring is equally manifest with gastric reflux and with deglutition of the gastric contents. Consequently, the centripetal pressure cannot be selected to be too high, or else it may cause an unacceptable impairment to swallowing. The absence of selectivity in this solution in terms of the direction of flow does not make it possible to guarantee total efficacy of this external prosthesis. It has also been found that the external prosthesis can be pushed upward by the pressure of gastric reflux, so that the base of the esophagus is again exposed to attack by the acidity of the gastric juices. This ring is located outside the esophagus, and so its position cannot be further modified by endoscopy. Shifts of this external prosthesis in the abdominal cavity limit its use and can have risks.
These disadvantages explain why the use of this prosthesis is not widespread, because it does not offer a sufficient guarantee. If it fails, then recourse to medication must be made anew, and the proportion of failures has proved to be high. Finally, there are also surgical procedures, in particular the Nissen-Rossetti fundoplicature, which comprises making a sleeve with the gastric fundus surrounding the cardia, under the diaphragm. The disadvantage of such an operation is that in the case of deficient esophageal peristalsis it may cause severe dysphagia. Still other surgical procedures exist. Nevertheless, all the surgical solutions have postoperative risks, such as a recurrence of reflux after relaxation of the sutures, dysphagia when the sleeve is too tight, and sliding of part of the stomach upstream of the sleeve, thus causing severe reflux esophagitis. The patient thus operated upon can also neither burp nor vomit, which is difficult for some patients to tolerate.
A prosthesis of an elastomer material has also already been proposed in U.S. Pat. No. 4,846,836, and is intended to be placed in the esophagus and includes a cone inside a tubular portion intended for fixation of the prosthesis. The cone has a slit apex and is aimed toward the stomach, comprising a sort of funnel that ends in a valve, the slit of which is intended to open by the peristaltic thrust exerted on the gastric juicealimentary bolus, but to prevent flow in the opposite direction. A second slit, made between the base of the cone and the tubular portion, is intended to open under a certain reflux pressure to enable vomiting.
A major disadvantage of this prosthesis is due to the fact that the alimentary bolus must pass through a substantially reduced cross section of the valve at the apex of the cone; this cone is necessary to enable flow in reverse for access to the second opening intended for reflux in the case of vomiting. It is clear that such a valve comprises a certain hindrance to the patient, who will have difficulty in swallowing, particularly solids, because of the shrinkage at the passage through the slit, which can cause pain that is difficult to tolerate.